This invention relates to an improved drill grinder and, more particularly, to a drill grinder of compact size and construction which includes a plurality of adjustments that make the grinder capable of sharpening various types, sizes and shapes of drills.
With continued use of a drill, particularly in commercial and manufacturing operations, it is necessary from time to time to sharpen that drill. Heretofore, rather expensive drill sharpening equipment has been provided. Often, such equipment is bulky, complex and expensive. Thus, it is desirable to provide a drill grinder capable of sharpening all types and shapes of drills.
In the past, the assignee of applicant has made a drill grinder which included a grinding wheel driven by an electric motor and a mounting assembly for holding a drill in position for engagement with the grinding wheel to shape the point of the drill. The mounting assembly includes an axial adjustment for setting the point angle of the drill bit. Also included is an adjustment for the size of the drill. Finally, a crude alignment feature for aligning the point of the drill is provided. The alignment feature is a means for arranging the drill in the proper rotational sense relative to the grinding wheel and thereby preserve the chisel edge angle of the drill.
While this prior art structure works quite well, it does not include any mechanism for setting the clearance angle for the point of the drill. The clearance angle is the angle between tangents to the cutting lip or leading edge of a drill and the trailing portion of the cutting lip surface. Preferably, the trailing surface or edge of the cutting lip surface should be somewhat lower than the leading edge. It should, however, not be too much lower since this would cause the cutting edges of the drill bit to break away. Another way of defining the clearance angle is by the radius of curvature of the cutting lip surface. This radius should decrease slightly in back of the leading edge or cutting lip of the drill.
Additionally, the prior art structure does not include any mechanism for maintaining the chisel edge angle for drills of all sizes. The chisel edge angle is the angle between the leading edge or cutting lip of the drill and the line defining the point of a drill.
To overcome these deficiencies in the prior art and simultaneously provide a structure having simplicity of design and ease of operation at low cost, the present invention was conceived.